1. Field of the Invention
The present invention relates to a system and method for controlling transmission power in a wireless local area network (WLAN), and more particularly, to a system and method for controlling transmission power in a WLAN, capable of providing WLAN service to terminals outside a service area by controlling the transmission power in the WLAN.
2. Description of the Related Art
A local area network (LAN) may be largely classified into a wired LAN and a wireless LAN. The largest difference between the two LANs is whether or not a cable is present.
In the wireless local area network (WLAN), communication is accomplished using radio waves instead of cable. The WLAN is now emerging as an alternative to overcome difficulties in installation, maintenance, and mobility due to the use of cable. In addition, the increasing mobility of users leads to an increasing need for the WLAN.
The WLAN is composed of an access point (AP) and a WLAN card. The AP is equipment which transmits radio waves so that WLAN users within a transmission distance can access the Internet and use the network. The AP also acts as a base station for cellular phones or a hub for a wired network. Similarly, for wireless high-speed Internet service, which is provided by an Internet service provider (ISP), AP equipment is already disposed in a service area.
For a current WLAN service, a WLAN user should associate with an access point (AP) disposed in a hot-spot region by using a terminal such as a notebook computer with a WLAN card, a personal digital assistant (PDA), or the like. Hereinafter, the wireless LAN terminal is referred to as a station (STA).
IEEE 802.11 is a wireless LAN standard which is widely used today and conforms to “Standard for Information Technology-Telecommunications and Information Exchange between Systems-Local and Metropolitan Area Networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” 1999 edition.
The IEEE 802.11 standard defines regulations relating to a physical layer and a medium access control (MAC) that constitute the wireless LAN.
The MAC layer defines an order and a rule with which a station or device using a shared medium should comply upon using/accessing the medium, in order to ensure efficient use of the medium capacity.
The WLAN, which is based on 802.11 MAC and IEEE 802.11a/b/g PHY, has been widely used in homes and offices.
In the IEEE 802.11, carrier sense multiple access with collision avoidance (CSMA/CA) is used for competitive occupation of a wireless channel and for communication. At this time, the intensity of radio waves transmitted over a wireless channel should meet a regulatory maximum transmission power (RMTP) requirement of the relevant country. For example, in South Korea, the intensity should not exceed 200 mW per channel. In the United States and Europe, the radio wave intensity is regulated for each frequency band.
However, in Europe, when IEEE 802.11a is used with a 5 GHz band, it is necessary to use transmission power control (TPC) and dynamic frequency selection (DFS) functionalities in order to first protect radar and satellite communications. In order to enact these technology standards, IEEE 802.11h TG is in use.
The TPC is a technique of using only necessary transmission power through control of the transmission power intensity to protect radar and satellite communications. Meanwhile, the DFS is a technique of switching a WLAN channel to another frequency band upon detection of a radar or satellite communication signal, in order to first protect an existing system.
The TPC has advantages in that it is capable of reducing radio wave interference between basic service sets (BSSs), and of efficiently managing a radio wave source, because the TPC is able to dynamically change a service range of a BSS by controlling the output of the AP, in addition to the advantage of protecting radar and satellite communications. In addition, the TPC is capable of reducing battery consumption by reducing the power consumption of stations.
In a system including stations outside a transmission power range of an access point (AP). When stations are positioned in a transmission power range of an AP, the stations may associate with the AP by recognizing their maximum transmission power permitted to transmit in a BSS (basic service set) from beacon information which is received from the AP.
However, a station positioned at a hidden node outside the transmission power range of the AP is unable to correctly receive the beacon information from the AP, which makes it difficult to associate with the AP.
In other words, since the AP is able to receive information from the station outside the transmission power range of the AP, but the transmission power of the AP is insufficient to reach the station outside the transmission power range of the AP, the station outside the transmission power range of the AP does not recognize the AP information. Accordingly, it is difficult to establish a communication link between the AP and the station outside the transmission power range of the AP.
Further, the AP has the disadvantage of high power loss because the AP maintains a certain transmission power all the time.
Incorporated by reference herein are U.S. Pat. No. 5,987,011 to Chai Keong Toh entitled ROUTING METHOD FOR AD-HOC MOBILE NETWORKS which discusses the use of beacons in an ad-hoc mode of communication between mobile stations in a network; and U.S. Pat. No. 6,859,656 to Joon-bo Choi et al. entitled APPARATUS AND METHOD FOR OPTIMIZING TRANSMISSION POWER OF NETWORK which discusses the use of connection information, which includes a reception signal strength and/or link quality information, in a communication unit that sends and receives a data packet through the air, wherein a control unit outputs a control signal for controlling the transmission power according to the connection information of the data packet received through the communication unit.